1. Field of the Invention
The invention relates to a method for producing a p-type SiC semiconductor single crystal.
2. Description of the Related Art
Practical applications of SiC semiconductors as high-voltage and high-current power semiconductors that are suitable for inverters or the like have been advanced because such semiconductors have better breakdown voltage characteristic, higher temperature resistance, and lower power loss than Si semiconductors. For example, metal oxide semiconductor field effect transistor (MOSFET) or insulated gate bipolar transistor (IGBT) constituting switching elements of inverters are required to have a low ON resistance and a high switching rate. Among n-type and p-type SiC semiconductors for constituting such transistors, the development of n-type semiconductors has been rather significantly advances, whereas the development of p-type semiconductors has been delayed. In particular a demand has been created for a method for producing a p-type SiC semiconductor single crystal at a growth rate necessary for practical use.
Various methods for growing p-type SiC semiconductor single crystals by a solution process have been suggested.
Japanese Patent Application Publication No. 2000-264790 (JP-A-2000-264790) discloses a method using a Si—C—Cr three-component solution prepared by adding Cr to a Si—C solution obtained by dissolving C in a Si melt, describes an exemplary solution composition of Si 23 at. %-C 23 at. %-Cr 54 at. %, and further suggests the possibility of obtaining a p-type SiC semiconductor single crystal by adding Al. However, no specific means for increasing the growth rate is suggested.
Japanese Patent Application Publication No. 2007-76986 (JP-A-2007-76986) discloses growing a p-type SiC semiconductor by a solution method, wherein using a Si—C—Ti—Al four-component solution obtained by complex addition of Ti and Al to a Si—C solution makes it possible to increase the growth rate to 180 μm/hr as an upper limit at which the single crystal growth can be stable. However, for practical use, the growth rate has to be further increased.
Further, as disclosed in Japanese Patent Application Publication No. 2004-2173 (JP-A-2004-2173) and Japanese Patent Application Publication No. 2006-143555 (JP-A-2006-143555), adding Ti increases the amount of precipitated SiC, but when Ti is added alone, polycrystallization is facilitated and stable single crystal growth is very difficult to perform. When Fe is added, the C dissolution effect in a Si melt is even higher than in the case of Ti addition, but the increase in the amount of precipitated SiC is small even when an oversaturation degree is increased by a temperature gradient.
Japanese Patent Application Publication No. 2005-82435 (JP-A-2005-82435), Japanese Patent Application Publication No. 2006-347852 (JP-A-2006-347852), and Japanese Patent Application Publication No. 62-69514 (JP-A-62-69514) disclose producing a p-type SiC semiconductor single crystal by adding Al to a Si—C solution, but no specific means for obtaining a high growth rate necessary for practical use is suggested.